Ischemia generally is a restriction in blood supply, with resultant damage or dysfunction of tissue. Ischemia refers to the absolute or relative shortage of blood supply to an organ. Relative shortage of blood supply means a mismatch of blood supply (oxygen delivery) and the need for adequate oxygenation of tissue.
Reperfusion injury refers to the damage caused to tissue when blood supply returns to the tissue after a period of ischemia. The absence of oxygen and nutrients from blood creates a condition in which the restoration of circulation results in inflammation and oxidative or peroxidative damage.